@bexley
I don't think they'd be using natural-born monkeys- more likely lab ones bred especially for testing. So there's far less of an issue with us plucking them from their natural surroundings and disrupting animal communities.
And the clever species is the one that adapts best to its environment- or adapts its environment to suit it. Which is us. The species that develops the ability to defend- and eventually all but rid- itself of predators. Groups that are not able or not willing to adapt (or just choose not to) as required are the "stupid" ones.
And when we spread to our next world- barring a sudden development of massive wormhole tech that lets us suit out habitable extrasolar planets- we'll have to develop our own ecosystem. We can't breathe on, say, Mars. So we'd need to create a self-sustaining, sealed environment to support ourselves.
As a side effect, this will give us technologies that will allow us to clean up the mess we've made on the Earth. CO2 scrubbers, mass clean power generation, the most effective material choices for recycling- all of these are things that'll be needed in the sealed environment of an offworld habitat or spacecraft. So we'll be the only race (that we know of) in the history of the universe who've developed to the point where they can actually clean up after themselves.
And none of us people saying use the protesters are going to step up because we have monkeys taking our place and would rather like to live to see the future Nasa's helping to create. Would you rather that they used humans? Maybe death-row inmates should be irradiated instead of being given a quick death (actually, this could be an interesting final-stage "is it definitely safe?" test)?
As for your second test, perhaps you'd prefer to see the monkeys just blasted until they die or blasted with radiation and released back into the wild (to be killed off)? If you accept that monkeys are being used- whether you agree or not they will be- then surely this is the best solution? And I'm sure if a post-trial monkey is able to they'll be provided with a branch or two to swing from.